A disc brake system provided with a brake disc and a brake pad has been widely used as the brake system attached to vehicles such as cars and motorcycles, enabling the braking of said vehicles. Such a disc brake system is configured so as to make it integrally rotatable with the vehicle by attaching the brake disc to the wheel of the vehicle such that it acquires the braking force by depressing the brake pad onto the brake disc.
Conventional brake discs, for example, include a brake disc having a rotor made of an approximately annular plate material and a tubular bracket attached at the center of the rotor, configured to acquire the braking force by attaching this bracket to the axle of the vehicle and depressing the brake pad onto the rotor. Such a conventional brake disc integrates the rotor with the bracket by fastening them via a fastening means such as a rivet. Furthermore, no prior art documentation is provided here as such prior art does not relate to the invention known to the public through publication.